12. CHEMICAL FACT SHEETS has a low acute toxicity. In short-term toxicity studies in rats, impairment of glutathi- one transferase activity and reduced glutathione concentrations were observed. In in vitro tests, styrene has been shown to be mutagenic in the presence of metabolic acti- vation only. In in vitro as well as in vivo studies, chromosomal aberrations have been observed, mostly at high doses of styrene. The reactive intermediate styrene-7,8-oxide is a direct-acting mutagen. In long-term studies, orally administered styrene increased the incidence of lung tumours in mice at high dose levels but had no carcinogenic effect in rats. Styrene-7,8-oxide was carcinogenic in rats after oral administration. IARC has classified styrene in Group 2B (possibly carcinogenic to humans). The available data suggest that the carcinogenicity of styrene is due to overloading of the detoxification mechanism for styrene-7,8-oxide (e.g. glutathione depletion).
Sulfate Sulfates occur naturally in numerous minerals and are used commercially, principal- ly in the chemical industry. They are discharged into water in industrial wastes and through atmospheric deposition; however, the highest levels usually occur in ground- water and are from natural sources. In general, the average daily intake of sulfate from drinking-water, air and food is approximately 500 mg, food being the major source. However, in areas with drinking-water supplies containing high levels of sulfate, drinking-water may constitute the principal source of intake.
Reason for not establishing Not of health concern at levels found in drinking-water a guideline value Additional comments May affect acceptability of drinking-water Assessment date 2003 Principal reference WHO (2003) Sulfate in drinking-water
The existing data do not identify a level of sulfate in drinking-water that is likely to cause adverse human health effects. The data from a liquid diet study with piglets and from tap water studies with human volunteers indicate a laxative effect at concentrations of 1000–1200 mg/l, but no increase in diarrhoea, dehydration or weight loss. No health-based guideline is proposed for sulfate. However, because of the gastro- intestinal effects resulting from ingestion of drinking-water containing high sulfate levels, it is recommended that health authorities be notified of sources of drinking- water that contain sulfate concentrations in excess of 500 mg/l. The presence of sulfate in drinking-water may also cause noticeable taste (see chapter 10) and may contribute to the corrosion of distribution systems.
2,4,5-T The half-lives for degradation of chlorophenoxy herbicides, including 2,4,5-T (CAS No. 93-76-5), also known as 2,4,5-trichlorophenoxyacetic acid, in the environment are in the order of several days. Chlorophenoxy herbicides are not often found in food.
419 GUIDELINES FOR DRINKING-WATER QUALITY
Guideline value 0.009 mg/l (9 µg/l) Occurrence Chlorophenoxy herbicides not frequently found in drinking-water; when detected, concentrations usually no greater than a few micrograms per litre TDI 3 µg/kg body weight, based on a NOAEL of 3 mg/kg body weight for reduced body weight gain, increased liver and kidney weights and renal toxicity in a 2-year study in rats, with an uncertainty factor of 1000 (100 for interspecies and intraspecies variation and 10 to take into consideration the suggested association between 2,4,5-T and soft tissue sarcoma and non-Hodgkin lymphoma in epidemiological studies) Limit of detection 0.02 µg/l by GC with ECD Treatment performance 1 µg/l should be achievable using GAC Guideline value derivation • allocation to water 10% of TDI • weight 60 kg adult • consumption 2 litres/day Assessment date 1993 Principal reference WHO (2003) Chlorophenoxy herbicides (excluding 2,4-D and MCPA) in drinking-water
Chlorophenoxy herbicides, as a group, have been classified in Group 2B (pos- sibly carcinogenic to humans) by IARC. However, the available data from studies in exposed populations and experimental animals do not permit assessment of the car- cinogenic potential to humans of any specific chlorophenoxy herbicide. Therefore, drinking-water guidelines for these compounds are based on a threshold approach for other toxic effects. The NOAEL for reproductive effects (reduced neonatal sur- vival, decreased fertility, reduced relative liver weights and thymus weights in litters) of dioxin-free (< 0.03 µg/kg) 2,4,5-T in a three-generation reproduction study in rats is the same as the NOAEL for reduced body weight gain, increased liver and kidney weights and renal toxicity in a toxicity study in which rats were fed 2,4,5-T (practically free from dioxin contamination) in the diet for 2 years.
Terbuthylazine Terbuthylazine (CAS No. 5915-41-3), or TBA, a herbicide that belongs to the chloro- triazine family, is used in both pre-emergence and post-emergence treatment of a variety of agricultural crops and in forestry. Degradation of TBA in natural water depends on the presence of sediments and biological activity.
Guideline value 0.007 mg/l (7 µg/l) Occurrence Concentrations in water seldom exceed 0.2 µg/l, although higher concentrations have been observed. TDI 2.2 µg/kg body weight, based on a NOAEL of 0.22 mg/kg body weight for decreased body weight gain at the next higher dose in a 2-year toxicity/ carcinogenicity study in rats, with an uncertainty factor of 100 (for interspecies and intraspecies variation)
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